Control system



Dec. 2, 1941. COOK 2,264,277

CONTROL SYSTEM Filed April 25, 1939 2 Sheets-Sheet l fig 1 Control/er WITNESSES:

' INVENTOR Willard 61'. 000k.

/' TTORNEY Dec. 2, W. G. COOK CONTROL SYSTEM Y Filed April 25, 1939 2 Sh eetsSheet 2 CaniroZ/er INVENTOR W/[ard 6 600%.

WITNESSES:

Patented Dec. 2,

CONTROL SYSTEM Willard G. Cook, Wilkinsburg, Pat, asslgnor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa.,' in, corporation of Pennsylvania Application April 25, 1939, Serial No. 269,906

Claims.

My invention relates, generally, to control systems, and, more specifically, to systems for controlling the acceleration and deceleration of the roll and reel motors of a strip rolling mill.

In the operation of strip rolling mills employed in the manufacture of steel strip, it is desirable that a controlled tension be applied to the strip as it passes through the reducing rolls. The application of tension to the strip produces a greater degree of reduction of the strip thickness for a given reducing roll pressure at each roll stand, and thus reduces the number of roll stands necessary to produce a given total strip reduction at a given roll pressure, or reduces the roll pressure necessary to produce a given strip reduction in a given number of roll stands. The application of tension to the strip while rolling also produces certain desirable characteristics in the strip material, such as uniformity of the structure of the strip and uniformity of gauge throughout the width of'the strip.

The amount of strip reduction for a given roll pressure is a function of the front and back tensions applied to the strip at the reducing rolls and for this reason, it is desirable that a substantially constant tension be applied to the strip to thereby secure uniform draft and produce a strip of uniform thickness.

As a pair of reducing rolls subjects a strip to reducing pressure and also subjects the strip to tension as it is delivered from the preceding roll stand, the total load on the motor driving the reducing rolls is comprised of components of friction load, tension load and rolling load while the speed of the rolls is constant. Since the friction and rolling loads are substantially constant for a given mill speed, it is only necessary to regulate the torque applied to the strip to produce uniform strip tension. This regulation of the strip tension has been accomplished in certain known strip rolling systems by a constant current regulator acting in response to the roll and reel motor armature current to control the motor field excitation.

While the mill is being brought up to speed, the total roll motor load is comprised of friction load, tension load, rolling load and acceleration load. If, then, the tension load is to remain constantduring all conditions of acceleration and running, it will be necessary to provide additional current loading of the motor during the acceleration. In a like manner, during deceleration, the motor load must be decreased to compensate for the power supplied by the inertia of the rolls and the motor. However, the acceleration and deceleration loads do not have a constant value throughout the acceleration and deceleration periods and it is necessary that the compensation be proportional to the rate 'of acceleration and deceleration in order to provide a substantially uniform tensioning load at all times.

Ingaddition to the variation in the acceleration and deceleration loads, the friction load varies as a function of the speed of the mill, and it is also necessary to compensate for this motor load variation in order to provide a substantially uniform tensioning load at all times.

An object of my invention, therefore, is to provide a control system which shall function to control the torque delivered by a motor.

Another objectof the invention is to provide a control system which shall function to control the power delivered by a motor.

A further object of the invention is to provide a motor control system which shall function to so control the load output of a motor which drives a work device as to cause a length of matei'ial which is being fed to and acted upon by thework device to be subjected to a substantially constant tension regardless of the speed and acceleration or deceleration of the work device.

Another object of the invention is to provide a control system for a strip rolling mill which shall function to so control the roll motor for a roll stand of the mill as to maintain a substantially constant tension on the strip as it is fed to the roll stand from the preceding roll stand regardless of the speed and changes of speed of the mill.

Still another object of the invention is to provide a control system for a strip rolling mill which shall function to so control a reel motor of the mill as to maintain a substantially constant tension on the strip as it is wound upon or unwound from the reel regardless of the speed and changes of speed of the mill.

These and other objects and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings in which:

Figure l is a diagrammatic view of an acceleration control system for a roll motor of a strip rolling mill embodying the principal features of my invention; and

Fig. 2 is a diagrammatic view of an acceleration control system for a reel motor of a strip rolling 4 and 4 for the roll stands 4 and HI. As the strip l2 passes between the roll stands in the direction indicated by the arrow, it is subjected to tension by the pulling action of the rolls of the roll stand Ill.

The tension on the strip I2 is maintained substantially constant by a regulator l4 which functions to vary the excitation of the motor 6 in response to variations of the load on the motor as measured by its armature current.

A pilot generator l6 driven by the motor 6 or by any suitable means at a speed proportional to that of the motor 6, is connected to vary the energiza-' tion of a solenoid-operated rheostat l4 through a transformer 20 in accordance. with the acceleration and deceleration'of the motor 4. The rheostat I8 is. connected to an operating circuit of the regulator l4 to vary thacalibration of the regulator l4 in accordance with changes of the speed of the motor 4 to thus permit the necessary variations of motor current during acceleration and deceleration to maintain substantially constant strip tension. The energization of the regulator is also varied in accordance with the speed of the mill motor 4 to compensate for variations of the friction load of the mill and its driving motor due to speed variations of the mill.

In the embodiment of the invention shown in by the rheostat I4, which is actuated by the pilot Fig. 2, the regulator I4 is automatically adjusted generator l4 through the transformer 20, and opcrates to control reel motor 4' to maintain the desired tension on the strip I! as it is received from'the roll stand 4 and wound upon the reel ll In this embodiment of the invention, the pilot -2 may be continuously driven at a substantially constant speedby any suitable motor or driving unit 22. The field winding 24 of the generator 2 is .energized from any suitable source of directcurrent power indicated by the bus A-B through a rheostat 24 which may be actuated to vary the energization of the field winding 24 and thus vary the output potential of the generator 2. The.

main generator 2 is connected to energize a main bus indicated by the conductors X-Y and the motors 4 and 4 are connected through suitable controllers as indicated to the bus X-Y.

The fleld windings I4 and 44 of the motors 4 and 4 are connected to be energized from the bus A-B-through rheostats 42 and 44, which may be adjusted to provide the base speeds for the motors 4 and 4. A resistance element 44 is also connected in circuit with the field winding 80 of the motor 4 and contact elements 44 and 40 of the regulator I4 are connected to the respective ends of the resistance element "by meansof conducto actuate the arm to move the contacteiement 38 into engagement with the contact element 44. A winding 42 is associated with the armature 44 and is connected to be energized in accordance with the armature current of the motor 4, ins

circuit which extends from one side of the series field winding 54 of the motor 4 through the conductor 56, a rheostat", a conductor 44, the winding' 52, a conductor 42, the resistance 44 of the rheostat l8, and a conductor 44 to the other side of the series field winding 44.

The resistance element 64 ofthe rheostat l4 has a series of taps as indicated, each connected to a different one of a series of spaced conducting leaf spring elements 44 which are suitably insulated from each other and have one and mounted in a fixed position. Each of the spring elements 66 has a contact element 44 mounted thereon, the contact elements 44 being so disposed as to provide a connection between each successive spring element and the adjacent spring element as a force is applied to the top spring element to deflect the spring elements downwardly. In their normal undetiected positions, the spring elements 66 are disposed with their ends engaging the member I4 of insulating material to hold them in a position with all of the contact elements 44 dis-' engaged. v

The stack of spring elements 44 may actuated to successively shunt out the desired numberv in turn, actuates a pin I4 engaging the topmostof the spring elements 46. The armature 14 of the solenoid I2 is normally biased by means of a spring 80 to permit all of the contact elements 44 to rest in the open circuit position. The winding 16 is connected to be continuously energized from the bus A-B through a rheostat 42, by which the amount of energization of the winding 14 may be adjusted. The energization of the winding 14 is such as to normally bias the armature 14 of the solenoid 12 to actuate a portion of the spring elements 64 to shunt out a portion of the sections of the resistance element 44, to thereby provide an increased or decreased effective resistance of the rheostat l4 by decreased or increased deflection of the spring elements 44. As indicated in tors 42' and 44, to provide a shunting circuit for the drawings, the three uppermost spring elements 44 have been actuated out of engagement with the element I4 to provide engagement of the contact elements 44 associated therewith, and thus shunting out the three uppermost sections of the resistance element 44.

' It will be understood that increased downward deflection of the spring elements 44 by increased actuation of the armature I8 will cause a shunting out of an increased number of sections of the resistance element 44 and that a decreased downward deflection will relieve the shunting circuit from successive sections of the resistance element 44. The winding-14 of the solenoid 12 is connected to be energized by the secondary winding 44 of the transformer 24 whose primary winding '44 is connected by means of conductors 44' and 44 i to the armature of the pilot generator II.

bus AB through a rheostat 44 by which the excitation of ,the pilot generator l4 may be ad;

' justed.

It will be understood from thiscircuit-arrangement that the winding 14 of the solenoid I! will be energized in accordance with the rate of change of the speed of the motor 6, since the secondary winding 84 of the transformer 20 will have potential induced in it only when the output potential of the pilot generator I6 is changing, due to acceleration or deceleration of the motor 6, and that the potential induced in the secondary winding 84 will be proportional to the rate of change of the speed of the motor 6. The polarity of the potential induced in the Secondary winding 84 will also depend upon the direction of the change in the speed of the motor 6, that is, it will depend upon whether the motor 6 is accelerating or decelerating, and the relation of the windings 14 and 16 is such as to cause thecoil I4 to buck the actuationof the armature 18 provided by the winding 16 when the motor 6 is accelerating to thus provide an increase in the eiiective resistance of the resistance element 64, and to add to th actuation of the armature 18 when the motor 6. is decelerating to thus decrease the efiective resistance of the resistance element 64.

Thus, it will be apparent in the operation of the system to energize the winding 52 of the regulator I4, that the winding 52 thereof will be energized proportionately with the armature current of the motor 6, but that the energizing effect upon the winding 52 will be varied by the rheostat I8 in accordance with the change of speed of the motor6 and in proportion to its rate ofchange of speed. I

The regulator I4 further comprises a fixed armature member 96 upon which are disposed windings 98 and I00. The winding I is continuously energized from the bus A-B through a rheostat I02, by which the degree of energization of the winding I00 may be selectively adjusted; The winding 90 is connected to be energized in accordance with the generated potential of the pilot generator I6 through a suitable rheostat I04 in a circuit which extends from one side of the generator I6 through the conductor 90, a conductor I06, the winding, 98, a conductor I08, the rheostat I04, a conductor H0 and the conductor 08 to the other side of the generator l6. Thus, it will be apparent that the regulator I4 is further adjusted in its operation in accordance with the speed of the motor. 6, since the output potential of the pilot generator I6 is proportional to the speed of the motor 6.

In the operation of the system, it will be understood that, with the motors 4 and 6 running at a constant speed, the torque developed by the motor 6 will be made up of components of the torque required to overcome the friction of the motor 6, the rolling load on the roll I0 and the tension load due to the tension applied to the strip I2 -as it is delivered from the roll stand 8 to the roll stand I0. Since for a given speed the rolling load and the friction load remain substantially constant, the tension load will remain constant if the total load of the motor is 'maintaincd constant. The regulator I4 operates to maintain the load on the motor constant by moving contact element 36 into engagement with contact 40 to thus increase the excitation of the motor 6 and tend to decrease its speed when the armature current of the motor 6 increases beyond a predetermined amount. This tendency to decrease the speed of the motor 6 will tend to decrease the output of the mot r 6 and thus decrease the tension on the strip if This operation of theregulator-H is intermittent and theexcitation of the motor 6 is continuously being increased and decreased to provide the proper adjustment of the excitation, the relative amounts of the increases and decreases of excitation of the motor 6 being controlled by the armature current of the motor 6 through the regulator I4.

If now it is desired to increase the speed' of the motors 4 and 6, the output potential of the main generator 2 may be increased by decreasing the effective resistance of the rheostat 26 to increase the armature potential of the motors 4 and 6. While the motors 4 and 6 are accelerating, the developed load of the motors will have to be increased anamount equal to the required accelerating torque if the torque applied to the strip I2 by the motor 6 in the form of strip tension is to be maintained constant, since the developed load of the motor 6 while it is accelerating, is equal to the tensioning load, the friction load of the motor and the mill I0, the rolling load, and the accelerating load. While this acceleration is taking place, the regulator I4 is readjusted or recalibrated to maintain a higher developed load on the motor 6, as hereinbefore described, through the actuation of the solenoid I2 by the change in speed of the motor 6 and, therefore, the output potential of the pilot generator I6 to increase the effective resistance of the resistance element 64 of the rheostat IB to thus permit a larger armature current to flow to produce a given adjusting effect of the regular tor I4 on the excitation of the motor 6. Since the acceleration component of the motor armature current is not directly proportional to the rate of acceleration of the motor, the different sections of the tapped resistance element 64 have diiferent resistance values so as to provide current adjustments of the regulator I4 corresponding to the rate of motor acceleration. It is to be understood that any number of sections of the resistance element 64 with their corresponding control contact elements 68 may be provided.

Since the friction load on the motor also increased with increase of the speed of the motor in the mill, it is necessary to readjust the regulator I4 to provide for this extra developed load' of the'motor 6, and this is provided as hereinbefore described, by the increased energization of the winding 98 of the regulator I4 by the increased output potential of the pilot generator I6.

In a similar manner, .when the mill is decelerated, the regulator I4 will be readjusted through the rheostat I8 by the decrease in output potential of the pilot generator I6 to compensate for the torque provided by the inertia of the moving parts of the motor 6 and the mill stand I0 to increase the effectiveness of the armature current of the motor 6 upon the regulator I4, and thus permit-the regulator I4 to maintain a lower output load on the motor 6, and at the same time provide the same amount of tensioning load upon understood that the rheostats 58 and I04 are provided for securing the proper adjustment of the energization of the coils of the windings in whose circuit they are connected, and that any equivac for the pilot generator 16 so long as such equivalent element provides a potential which is proportional to the speed of the motor 6.

In the embodiment of the invention shown in.

Fig. 2, the system is substantially the same as that of Fig. 1, except that the winding tension on the strip I2 is regulated by the control of the motor 6' which drives the reel ll The energization of the field winding 30' of'the motor 8' is controlled by the regulator I in the manner explained hereinbefore in connection with the operation of the regulator I4 to control the roll motor 6 of the embodiment of Fig. 1. Likewise, the coil 52 of the regulator H is connected to be energized by the potential drop across the series field winding 54. I

The pilot generator 16 is driven by the roll motor 4 instead oi-the motor 6' whose output it controls in this embodiment of the invention, since the speed of the roll stand 8 is a measure of the strip speed as it is wound on the reel I I.

means in accordance with the motorspeed,

whereby the torque delivered by the motor to the load is maintained substantially constant throughout a desired range of motor speed.

3. In a control system for maintaining the torque delivered by a motor to a load to which it is connected substantially constant throughout a desired range of speed of the motor, means re-- sponsive to the motor speed for. varying the friction component of the developed motor torque in accordance with the rate of speed of the motor, and motor speed controlled means responsive to the motor acceleration and deceleration for vary- The speed of the motor 6' is not a measure of the strip speed since the speed of thereel II is v continuously varying because of the build-up" of strip on the reel.

The embodiment of the invention of Fig. 2 is also applicable to the control of the tension on the strip at the unwinding reel. In applying the system to the unwinding reel, the reel motor acts as a drag generator, or regenerative brake, and the pilot generator [6 is connected to be driven by the roll motor of the first roll stand.

While the system herein shown has been described as operating in connection with a strip rolling mill, it is to be understood that it is equally applicable to any system in which work devices operate upon a strip or web as it passes therethrough and apply tensions to the strip or web such as printing machines, papermanufacturing apparatus or cloth manufacturing or working machines. It will be seen that I have provided a motor control system which shall function to so control the load output of a motor which drives a work device as to cause a length of material which is fed'to and acted upon by the work device, to be subjected to a substantially constant tension regardless of the speed and acceleration or deceleration of the work device, which is simple and eflicientin operation and inexpensive to manufacture, install and maintain.

In compliance with the requirements of the patent statutes, I have shown and described herein a preferred embodiment of my invention. It is to be understood, however, that the invention is not limited to the precise constructions shown herein, but is capable of modification by one skilled in the art, the embodiment herein shown and described being merely illustrative of the principles of my invention.

I claim as my invention: 1

1. In a system of control for a motor connected to a source of energy and driving a load, control means responsive to the load, the speed, and acceleration and deceleration of the motor for so controlling the excitation thereof as to maintain the torque delivered by the motor to the load at substantially constant value regardless of changes in motor speed.

2. In a system of control for a motor connected to a source of energy and driving a load, regulator means responsive to the armature current of the motor for controlling the excitation of the motor, motor speed controlled acceleration .and deceleration responsive means for varying the ing the acceleration and deceleration component of the developed motor torque in accordance with the rate of acceleration and deceleration of the motor whereby the delivered motor torque will remain substantially constant throughout the desired range of motor speed.

4. In a motor control system, regulator means responsive to the armature current of the motor for maintaining the developed torque of the motor substantially constant for a given motor speed, a transformer, means responsive to the motor speed for continuously energizing the primary winding of said transformer with a direct current potential proportional to the speed of the motor, and means responsive to the potential induced in the secondary winding of said transformer for causing said regulator means to vary the developed motor torque in accordance with the acceleration and deceleration of the motor.

5. In a control system for maintaining the torque delivered by a motor to a load to which it is connected substantially constant throughout a desired range of speed of the'motor, means responsive to the motorspeed forvarying the friction component of the developed motor torque in accordance with the rate of speed of the motor, and means responsive to the motor speed for varying the deceleration and/or acceleration component of the developed motor torque the friction component of the developed motor torque in accordance with the rate of speed of the motor, and means responsive to the motor speed for varying the component of the devel oped motor torque required for changing the speed of the motor in accordance with the rate of acceleration and/or deceleration of the motor whereby the delivered motor torque will remain substantially constant throughout the desired range of motor speed. '7. In a motor control system, regulator means responsive to the armature current of the motor for maintaining the developed torque of the motor substantially constant for a given motor speed, a transformer, means for continuously energizing the primary winding of said transformer with a direct-current potential proportional to the speed of the motorrmeans responsive to tor substantially constant for any constant motor speed, a generator having a constant excitation and driven at a speed proportional to the speed of the motor, a transformer having its primary winding connected to be energized by said generator, means responsive to the potential induced in the secondary winding of said transformer for causing said regulator means to vary the developed motor torque in accordance with the rate of variation of the motor speed, and means responsive to the generator potential for causing said regulator means to vary the developed motor torque in accordance with the rate of speed of the motor.

9. In a motor control system for a strip rolling mill, a reducing roll stand comprising reducing rolls operative to subject a strip of material to tension as it is fed to the rolls, a driving motor for the reducing rolls, regulator means responsive to the armature current of the motor for controlling the excitation of the motor,

means responsive to acceleration and deceleration of the motor for varying the energizing effect per unit of the motor armature current upon said regulator means, and means responsive to the speed of the motor for varying the energization of said regulator means, whereby the tension applied to the strip by the motor is maintained substantially constant throughout a desired range of motor speed.

10. In a motor control system for a tandem strip rolling mill, a drive motor for the first roll stand and a drive motor for each of. the succeeding roll stands, means for simultaneously varying the speeds of said motors by armature voltage control, and control means for each of said succeeding roll stand motors, comprising, regulator means responsive to the motor armature current for controlling the excitation of the motor, means responsive to acceleration and deceleration of the motor for varying the energizing effeet per unit of the motor armature current upon said regulator means, and means responsive to the speed of the motor for varying the energization of the regulator means, whereby the tension applied to the strip by each of said succeeding motors is maintained substantially constant throughout a desired range of motor speed.

11. In a. control system for a plurality of drive motors each of which drives one of a plurality 'of work devices which simultaneously act upon a' strip of "material as each succeeding work device subjects the strip of material to tension as it is .drawn into the work device, means for simultaneously varying the speeds oi the motors by armature voltage control, and control means for each succeeding motor, comprising, regulator means responsive to the motor armature current for controlling the excitation of the motor, means responsive to. acceleration and deceleration of the motor for varying the energizing eiIect per unit of armature current upon said regulator means. and means responsive to the speed of the motor for varying the energization of the regulator means, whereby the tension applie'djto the length of material by each of the succeeding drive motors is maintained substantially constant throughout a desired range of motor speed.

12. In a control system for the drive motor of a strip rolling mill, regulator means responsive to the armature current and controlling the excitation of the motor for maintaining the developed torque of the motor substantially constant for a given motor speed, a transformer, means for continuously energizing the primary winding of said transformer with a direct-current potential proportional to the speed of the motor, means responsive to the potential induced in the secondary winding of said transformer due to changes in the energization of the primary winding for causing said regulator, to vary the developed motor torquein accordance with the rate of vari-' ation of the motor speed comprising a rheostat connected to vary the effect per unit of armature current on said regulator means, electromagnetic means energized by the secondary of said transformer for varying the rheostat setting in accordance with the change in the motor speed, and means responsive to the potential applied to the primary winding of said transformer for causing said regulator means to vary the developed motor torque in accordance with the rate of speed of the motor.

13. In a system of control for a motor driving a work device which operates to tension at length of material as .it is fed to the work device, regulator means responsive to the armature current of the motor for maintaining the developed torque of the motor substantially constant for a given motor speed, a transformer, means responsive to the motor speed for continuously energizing the primary winding of said transformer with a direct current potential proportional to the rate of feed of the material to the work device, means responsive to the potential induced in the secondary winding of said transformer for causing said regulator to vary the developed motor torque in accordance with the rate of variation of the rate of feed of the material to the work device, and means responsive to the potential applied to the primary winding of said transformer for causing said regulator means to vary the developed motor torque in accordance with the rate of feed of the material to the work device.

14. In a system of control for a motor driving a work device which operates to tension a length of material as it is fed to the work device, regulator means responsive to the armature current of the motor for maintaining the developed torque of the motor substantially constant for any constant motor speed, a generator havinga substantially constant excitation, means driving the generator at a speed proportional to the rate of feed of the length of material to the work device, a transformer having its primary winding connected to be energized by said generator, means responsive to the potential induced in the secondary winding of said trans former for causing said regulator means to vary the developed motor torque in accordance with the rate of variation of the rate of feed of the material to the work device, and means responsive to the generator potential for causing said regulator means to vary the developed motor torque in accordance with the rate or feed of the length of material.

15. In a system of control for a motor driving a work device which operates to tension a length of material as it-is fed to the work device, regulator means responsive to the armature current of the motor for maintaining the developed'torque of the motor substantially constant for any constant motor speed, a transformer, means for continuously energizing the primary winding of said transformer with a direct current potential proportional to the rate of feed of the length of material to the work device, means responsive to the potential induced in the secondary winding of said transformer due to changes in the energization of the primary winding for causing said regulator to vary the developed motor torque in accordance with the 15 oi feed of the length of material to the work device.

WILLARD G. COOK. 

